Refrigerator compressor



July 2, 1957 M. Y. WARNER REFRIGERATOR COMPRESSOR 3 Sheets-Sheet 1 Filed July 16, 1953 .272 z/en for. %Z'Zf0 72" If; mam Q ffl y,

I July 2, 1957 M. Y. WARNER 2,797,857

REFRIGERATOR COMPRESSOR Filed July 16, 1955 3 Sheets-Sheet 2 Mi'ZfOn K Merrie? July 2, 1957 M. Y. WARNER 2,797,857

REFRIGERATOR COMPRESSOR Filed July 16, 1953 3 Sheets-Sheet 3 k\\ &

Wiiian Y War a? REFRIGERATOR CUMPREETSQR Milton Y. Warner, Evansville, Ind, assignor, by assignments, to Whirlpool-Sanger Corporation, a corpnration of Deiaware Application July 15, 1953, Serial No. 363,293

2 Claims. (Ci. teees This invention relates generally to motor-compressor units, and more specifically to an improved hermetic motor-compressor unit for use in a refrigeration system wherein the motor is of the axial air-gap type.

Hermetic motor-compressor units find important use in the refrigeration art, and it is of further importance in that art that these hermetic motor-compressor units have as narrow a width as possible to permit the design of refrigerator cabinets wherein only a small proportion of the available space need be allotted to the motorcompressor unit. One of the chief advantages of an axial air-gap motor is the narrow width of the motor as measured parallel to the axis of rotation. Compared to a conventional motor of similar horsepower this dimension is considerably less. Therefore the object of this invention is to provide a hermetic motor-compressor unit wherein the motor is of the axial air-gap type and wherein the hermetic unit has a possible width substantially less than is possible with the hermetic motor-compressor units presently known in the art.

It is a feature of this invention that a novel oil pump and thrust hearing are provided which maintains the Width of the assembly within narrow limits.

It is another feature of this invention that a novel arrangement is provided for lubricating the cylinder of the compressor portion of the unit.

It is a further feature of this invention that a novel counterweight is provided with novel means for mounting the counterweight to balance the crankshaft.

It is another feature of this invention that novel structure is provided for suspending the motor and the compressor within the hermetic casing with means for adjustment of the suspension.

It is a further feature of this invention that a novel snubber is provided to prevent unnecessary vibration of the outlet line of the compressor.

Other objects and features of the present invention will be apparent upon a perusal of the following specification and drawings of which:

Figure 1 is a top plan view of the unit with the upper part of the casing removed;

Figure 2 is a cross sectional view of the assembly shown in Figure 1 taken along the line 22;

Figure 3 is an exploded isometric view of the combination oil pump and thrust bearing;

Figure 4 is a diagrammatic view of the snubber arrangement for reducing unwanted vibrations of the outlet line of the compressor; and

Figure 5 is a plan view of the counterweight for balancing, the crankshaft.

The. present embodiment is the preferred embodiment, but it is to be understood that changes can be made in the present embodiment by one skilled in the art without departing from the spirit and scope of this invention. Generally, the motor. and the compressor are mounted 2,797,857 Patented July 2, 1957 2 casing. Referring to Figure 2, the axial air-gap motor comprises substantially the lower half of the structure shown therein and the compressor comprises substantially the upper half of the structure shown therein. The motor is generally designated with the character 13 and the compressor is generally designated with the character 12. The motor is generally mounted within and supported by a substantially bowl-shaped stator support frame 14, and the compressor 12 is generally mounted within and supported by a substantially bowl-shaped crankcase 15. The crankcase 15 and the stator support frame 14 are rigidly connected together by three bolts 16, which project through three holes 17 provided in the periphery of the crankcase 15, and which are threaded into three tapped holes 18 in the periphery of the stator support frame 14. The three bolts 11% are triangularly disposed to each other as can be easily seen in Figure 1. A spring hook 19 is attached to the top of the crankcase 15 by the bolt 16, as can be :seen in Figure 2. Two other spring hooks 19 are provided which are mounted to the crankcase 15 by the other two bolts 16. It is intended that the unit be mounted longitudinally in a horizontal plane with the compressor portion 12 disposed above the motor portion 13. The internal assembly is resiliently suspended by three suspension members 21 Each of these suspension members 2t) comprises a mounting element 21, a coiled spring 22, and a spring hanger 23. The mounting element is connected to the underside of the upper pan 11. To the mounting element 21, the spring hanger 23 is rigidly connected. The spring hanger 23 is generally cone-shaped, and the portion thereof which is adjacent to the mounting element 21, has a number of threads formed thereon which are complementary to the turns of the coiled spring 22. Thus the upper end of the coiled spring 22 is mounted over and threaded onto the spring hanger 23. The lower portion of the coiled spring 22 is formed to have a hook thereon. This hook is mounted in cooperation with the spring hook 19 to thereby resiliently suspend the motor-compressor unit within the casing. Since the coiled spring 22 is threaded onto the spring hanger 23, it may easily be seen that the effective length of the coiled spring 22 may be increased or decreased by threading and unthreading the coiled spring 22 on the spring hanger 23 in increments of For lubrication and cooling of the unit a quantity of lubricating oil is provided. The lubricating oil 24 is disposed within the lower pan ltl as can be easily seen in Figure 2, and the amount used is that amount sufficient to substantially submerge the motor 13.

The motor 13 will be described in detail first. As previously noted, the motor is generally supported and contained within a bow-shaped stator support frame 14. The stator 25 is rigidly connected to the concave side of the stator support frame 14 by means of bolts 26 The stator 25 includes the field windings 9 which are connected to a cable 8. The cable 8 is in turn connected Without the lower pan 10 by the terminal assembly 17. A hearing 27 is provided through the center of the stator support frame 14, and within this hearing 27 the crankshaft 28 is rotatively mounted. The center portion of the convex side of the stator support frame 14 is generally formed with a depression therein. The tip of the crankshaft 28 projects into this depression and a number of holes 29 are formed through the stator support frame 14 from the concave side thereof into the depression. The depression is enclosed by the oil pump and thrust bearing means which are shown generally with the character 30. The portion 31 of the depression of the stator support frame 14 is formed with an involute curve.

The rotor for the motor is shown generally with the character 32. The portion of the crankshaft 237which cooperates with the rotor 32 is shaped to have a hub 34 E and a ring 35. The hub 34 and the ring 35 are tapped for four bolts 36. The rotor 32 is mounted over the hub 34 and against the ring 35 with a light press fit. The major proportion of the rotor 32 is fabricated as a continuous strip of steel wound in a roll and integrally cast with two rings of aluminum and with aluminum bars passing through the steel. The roll of steel 37 has radial holes about its periphery and upon casting the aluminum completely fills these holes to form an integral part with the roll of steel. The inner aluminum ring is tapered as shown at 38. The complete assembly of the rotor also comprises a rotor support disk 39 and a spacer ring 40. The rotor support disk 39 has four holes therethrough which are aligned for cooperation with the bolts 36. When the rotor 32 is mounted to the crankshaft 28, the bolts 36 are tightened to cause the rotor support disk 39 to be bent against the rotor spacer ring 40 and the bevel 38 of the inner aluminum ring of the rotor 32.

For a description of the oil pump and thrust bearing reference is made to Figures 2 and 3. The oil pump and thrust bearing 30 comprises the impeller retainer 44, the impeller 45, the thrust plate facing 46, and the plate 47. The crankshaft 28 is formed with a hole 42 extending axially therethrough. The crankshaft 28 is further formed to have two notches 43 formed at the one end thereof which is disposed within the depression formed within the convex surface of the stator support frame 14. The impeller retainer 44 is formed of a rectangularly shaped material with two prongs extending upward therefrom. The two prongs of the impeller retainer 44 are pressed into the two notches 43 on the end of the crankshaft 28 to thereby maintain the impeller retainer 44 thereagainst. The impeller retainer 44 also has a hole through the center thereof and this hole cooperates with the bore 42 in the crankshaft 28. The impeller 45 is generally circular in shape, and has a plurality of vanes extending from the circular surface thereof, as can easily be seen in Figure 3. The impeller 45 is mounted in cooperation with the impeller retainer 44 so that the edges of the impeller retainer 44 are pressed between the vanes of the impeller 45. The impeller 45 also has a hole formed through the center thereof which cooperates with the hole through the center of the impeller retainer 44 and the bore 42 of the crankshaft 28. The impeller 45 when so mounted operatively cooperates with the involute curve formed within portion 41 of the depression on the convex side of the stator support frame 14, so that any liquid fed centrally of the impeller 45, when the crankshaft 28 is rotating, will be forced outwardly from the vanes of the impeller 45 and in the involute curve. The thrust plate facing 46 which is formed of a hard metal, and the thrust plate 47 are mounted together and rigidly connected over the depression in the convex side of the stator support frame 14. The thrust plate facing 46 is mounted between the thrust plate 47 and the stator support frame 14. The thrust plate facing 46 and the thrust plate 47 are rigidly mounted over the depression on the convex side of the stator support frame 14 by four bolts 48 which project through four holes in the thrust plate facing 46 and the thrust plate 47, and are threaded into four tapped holes in the stator support frame 14. The thrust plate facing 46 is further formed to have four holes 49 formed therethrough, and these holes 49 are positioned beneath the vanes of the impeller 45. The thrust plate facing 46 is further formed to have four slots 50 formed therethrough. The four slots 50 intersect each other at an opening in the center of the thrust plate facing 46, as can easily be seen in Figure 3. These slots 50 are positioned beneath the circular flat portion of the impeller 45. The thrust plate 47 has four channels 51 formed therein. These channels 51, which are substantially wider than the slots 50, and which may easily be seen in Figure 3, are so positioned as to intersect at an opening in the center thereof. Each of the slots 51 are formed of a length equal to the length of each of the slots 50 plus the distance from the end of each of the slots 59 to the outermost side of the holes 49. The slots 50 of the thrust plate facing 46 are not centered directly above the channels 51 in the thrust plate 47, but are positioned off-center thereof in a direction dependent upon the direction of rotation of the impeller 45. Assuming for purposes of explanation that the impeller is rotating in a counterclockwise direction as viewed in Figure 3, then the side 54 of each of the slots would be the leading edge of these slots and the side 53 of each of these slots would be the trailing edge of these slots. The slots 50 are then positioned in relation to the channels 51 so that the leading edge of each of the slots 50 is positioned upon the center line of each of the channels 51. Thus the leading edges of each of the slots 50 overhang the channels 51 a substantially greater amount than do the trailing edges of each of the slots 50. Thus when the motor 13 is operating, the thrust exerted by the crankshaft 28, due to the magnetic attraction between the rotor 37 and the stator 25, will be distributed throughout the area between the impeller 45 and the thrust plate facing 46, and the thrust plate facing 46 will act as thrust shoe. Now if oil is supplied to the channels 51, a wedge-shaped film of oil will be formed between the trailing and leading edges of the slots 50 as the crankshaft 28 is rotating. This will result in a lubrication of the thrust bearing similar to that supplied by the well known Kingsbury thrust bearing. To discuss the operation of the oil pump, when the crankshaft 28 is rotating, the oil 24 disposed within the lower paf1*10 will flow into and through the holes 29 in the stator support frame 14. This oil will flow into the space centrally of the impeller 45. The rotating impeller 45 will move the oil radially thereof into the vanes thereof. From the vanes of the impeller 45, the oil will flow downward through each of the openings 49 in the thrust plate facing 46. From the openings 49, the oil will flow into and through the channels 51 of the thrust plate 47. From the channels 51 of the thrust plate 47, a portion of the oil will flow upward through the center thereof, through the center of the thrust plate facing 46, through the hole in the center of the impeller 45, through the hole in the center of the impeller retainer 44 and into and through the bore 42 of the crankshaft 28. Another portion of the oil flowing through the channels 51 will flow upward through the slots 50 to lubricate the thrust bearing previously described.

To discuss the detailed structure of the compressor 12 reference is made to Figures 1 and 2. The crankcase 15 comprises a substantially bow-shaped casting, which as previously described is mounted to the peripheral edge of the stator support frame 14 by the bolts 16. To further aid in the alignment of the crankcase 15 with the stator support frame 14 three dowels 55 are provided. A bearing 56 is formed through the center of the crankcase 15 as can easily be seen in Figures 1 and 2. The bearing 56 supports the upper end of the crankshaft 28. The bore 42 extends upwardly through the crankshaft 28 and near the upper end thereof is formed to slant away from the axis of rotation of said crankshaft 28 as can be seen in Figure 1. Thus when the crankshaft 28 is rotated by the motor 13, the oil which flows from the oil pump 30 upward through the crankshaft 28 and out of the top thereof is given a lateral component of motion. Thus as the crankshaft 28 rotates, the oil is sprayed about the inner surface of the upper pan 11 and will then flow downward along the inner walls of the casing to the lower pan 11. As the oil flows along the inner surfaces of the casing, heat from the oilwill be conducted to the casing thereby coolingthe oil. ,The crankshaft 28 is further provided with an eccentric 57 formed as a part thereof. A channel 58 is formed through the eccentric 57 to the bore 42 of the crankshaft 28 to provide lubrication for the eccentric 57. A further channel 59 is formed radially from the bore 42 to the outer surface of the crankshaft 28 which is disposed within the bearing 56. The oil flowing through the channel 59 serves tolubricate the bearing 56. and the cylinder 60. The specific structure cooperating with the channel 59 to provide lubrication for the cylinder 60 includes a depression 61 formed in the upper surface of the crankcase 15, and two holes 62 and 63. The hole 62 is formed in the crankcase 15 from an upper portion of the depression 61 into the bearing 56 and in vertical alignment with the channel 59. The hole 63 is formed through the crankcase 15 from the lowest portion. of the depression 61 downward into the cylinder 6%. Whenever the crankshaft 28 is rotated to the position wherein the channel 59 is in horizontal alignment with the hole, 62, oil flowing upward through the bore 42 will flow through the channel. 59, through the hole 62into and fillingthe depression 61. Fromthe depression 61 the oil will flow downward through the hole 63 into the cylinder 66. The cylinder 60 is cast as an integral portion of the crankcase 15 on the concave side thereof as can be easily seen in Figure 2. The cylinder 66 is further formed so that the longitudinal axis thereof is at a right angle to the axis of rotation of the crankshaft 28. A piston 64 is slidably mounted within the cylinder 60. A connecting rod 65 is rotatively mounted about the eccentric 57 and is pivotally connected to the piston 64 by a Wrist-pin 66, as can be easily seen in Figure 2. It can thus be seen that as the motor 13 is operated to rotate the shaft 28, the piston 64- will operate within the cylinder 66, and oil will flow from the hole 63 to lubricate the piston 64- and, the cylinder 6% A cylinder head 67 is mounted over the cylinder 66 in cooperation with the piston 64. The cylinder head 67 is mounted to the crankcase 15 by means of the bolts 68. Within the cylinder head 67 intake and exhaust valves 6% are mounted. These valves may be of any type well known in the art, and therefore the construction thereof will not be described in detail. The crankcase 15 is further provided with two muffler chambers 7t) and 71. These muilier chambers '70 and 71 are cast as integral parts of the crankcase 15, the muffler chamber 79 serving as an intake mufiier and" the muffler chamber 71 serving as an exhaust muffler. A hole 72 in the top of the muffler chamber 70 is provided when the crankcase 15 is cast to aid in the casting thereof. This hole 72 is sealed by a plug 73. A hole 74 is formed through an end wall of the muffler chambers 71 to aid in the casting thereof and to serve as an outlet from the muffler chamber 71. An opening '75 is formed through one wall of the muffler chamber '76. This hole 75 is formed on the concave side ofthe crankcase 15-, so that refrigerant gases. are drawn into the mufiler chamber 70 through the hole 75, from the concave side of the crankcase 15, from the open spaces about the periphery of and between the crankcase 15 and the stator support frame 14, and from a tube 7 6 connected through the upper pan 11 of the casing. Any refrigerant gases which enter the muffler chamber 70 are delivered to the cylinder head 67 and the cylinder 60 through a channel 77 formed through the crankcase .15. from the mufiier chamber 70 to the cylinder head 6.7. The exhaust muffler chamber 71 is connected to the cylinder head 67 and the cylinder 66 by means of a channel 78 extending from the exhaust muffler chamber 71 to the cylinder head 67. An exhaust muffler chamber cover 79 is provided over the opening 74 of the exhaust mutfler chamber 71. To the exhaust mufiier chamber cover 79, a length of tubing 80 is connected. This length of tubing 36 extends from the exhaust mufller chamber cover 79 about the inside of the upper pan 11 in one complete turn, and is then connected without the upper pan 11 by means of the tube 82. A bolt 83 extends through the exhaust mufiler chamber cover 79 to maintain the exhaust muffler chamber cover 79 against the opening 74. This bolt 83 is threaded into a tapped hole in the crankcase 15.

To next describe the operation of the compressor 12, when connected in a refrigeration system, (not shown) refrigerant gases are drawn into the tube 76 between the peripheral edges of the crankcase 15 and thestator support frame 14, within the concave side of the crankcase 15, into and through the hole. 75, into theintake muffler chamber 70, through the tube 77, into the cylinder head 67 and the cylinder 60, through the cylinder'head 67 into and through the tube 78, into the. muffler chamber 71, through the hole. 74. into the exhaust muflier chamber cover 79, through the tubing and out of the unit through the length of tubing 82.

To balance the crankshaft 28, a specific counterweight S4 is provided. A plan view of the counterweight 84 can be seen in Figure 5, and a cross-sectional view thereof taken along the line 2'-2 can be seen in Figure 2. The counterweight 8.4 is formed in the general shape. of a semi-circular ring. The lower portion of the inner periphery of the counterweight 84 is formed with a bevel 85 as can be seen in Figure 2. The crankshaft Z8 is further shapedto have a circular beveled portion 33; The bevel 85' of the counterweight 84 matches the beveled portion 33 of the crankshaft 28. The outer periphery of the counterweight 84 is formed with two slots 86 therein. These slots.86 are spaced apart a distance equal to the spacing between'two of the bolts 36 which maintain the rotor 32. mounted to the crankshaft 28. The counterweight 84 is further provided with a counterbored hole 87. Further, a portion of the hub 34, between the aforementioned two bolts 36, is tapped so that a bolt 88 may be projected through the hole 37 and threaded thereinto. When the counterweight 84 is mounted to the crankshaft 28, the two bolts 36 are positioned within the two slots 86 and the bevel. 85 cooperates with the beveled portion 33, and as the bolt 88 is tightened, the counterweight 84 isforced downward and outward until the two bolts 36 are tightly wedged against the two slots 86.

As previously described, the discharge line or length of tubing 80' is connected to the exhaust mufiier cover 79, and is further brazed to the length of tubing 82, and is positioned to make a complete loop about the inside of the upper pan 11. The purpose of this loop is to provide sufiicient flexibility in the discharge line connection between the compressor 12 and the upper pan 11 so as to allow freedom of movement of the motor-compressor unit with respect to the casing. To dampenany resonant vibrations that may .occur in the discharge line 80, a snubber spring 90 is provided. The snubber spring 90 is held by spring action between the discharge line 80 and one of the springs 22 of one of the hanger assemblies 20. As shown, the snubber spring 90 is positioned approximately midway of the discharge line 80 and midway of the coiled spring 22. Thus a point located midway on the coiled spring 22 moves, with respect to the casing, approximately one-half the distance that the motor compressor assembly moves. The midpoint on the discharge line 80. will likewise move about one-half the distance that the motor-compressor assembly will move. Thus movement of the motor-compressor assembly with respect to the casing is not restrained by the snubber spring 90, but any vibration that occurs in the discharge line 80, otherthan the forced vibration at the frequency at which the motor-compressor assembly is vibrating will. be opposed by the restraining action of the snubber. For a detailed description of the operation of the snubber spring 90 reference is made to Figure 4 wherein the structure is shown diagrammatically. As shown the motor-compressor unit 12 and 13 is free to vibrate in any direction. It can be seen that the use of the snubber spring 90 upon the discharge line 80 does not interfere with the normal movements of the motorcompressor unit 12 and 13 indiced by unbalance of moving parts and by variations in torque load. In relation to the vibrations of the motor-compressor unit 12 and 13, it may be seen that if the flexible discharge line 80 should happen to be resonant or near resonance to some disturbing frequency, at some load condition, the discharge line 80, between the ends thereof, might vibrate at a greater amplitude or at a dilferent' phase than the end of the loop fastened to the compressor. This condition would produce relative motion between the tube loop and the coiled spring 22. The snubber spring 90 connected between the discharge line 80 and the coiled spring 22, between the ends of the discharge line 80, would exert frictional restraining forces upon such rela tive motion.

Having described the invention what is considered new and desired to be protected by Letters Patent is:

1. In a device of the class described, a stator, a stator support, a crankcase, a cylinder formed in said crankcase, a piston slidably mounted in said cylinder, an eccentric, a rotor, a shaft, said stator support and said crankcase mounted together at the peripheries thereof, said stator support and said crankcase each formed to have a bearing therein, said shaft rotatively mounted in said bearings substantially at the ends of said shaft, said stator rigidly mounted to said stator support between said stator support and said crankcase, said rotor rigidly mounted to said shaft between said stator and said crankcase said eccentric rigidly mounted to said shaft between said rotor and said crankcase, and means movably connecting said piston to said eccentric, said shaft formed to have a beveled portion thereon adjacent to said rotor, said rotor having a pair of projections thereon adjacent to said shaft, a counter-weight for balancing said shaft, said counter-weight formed to substantially the shape of a semicircular ring, a pair of slots in the outer periphery of said counter-weight for cooperation with said projections on said rotor, said counter-weight further formed to have a beveled edge on an inner circumference thereof for cooperation with said beveled portion on said shaft, said counter-weight further formed to have a hole therethrough, a bolt projecting through said hole in said counter-weight and being threaded into said rotor, so that said pair of slots in said counter-weight are forced against said projections by the cooperating bevels of said counter-weight and said shaft when said bolt is tightened.

2. In a device of the class described, a sealed casing comprising an upper substantially bowl-shaped pan and a lower substantially bowl-shaped pan, a motor-compressor unit mounted within said casing, means attached to the inner surface of said upper pan and to said motorcompressor unit for resiliently suspending said motorcompressor unit within said casing with the compressor portion of said unit positioned vertically above the motor portion of said unit, a certain quantity of oil disposed within said lower pan substantially submerging said motor, said compressor portion comprising a substantially bowl-shaped crankcase, said motor portion comprising a substantially bowl-shaped stator support, mounting means connecting the peripheral edge of said crankcase to the peripheral edge of said stator support, said crankcase having a cylinder formed on the concave side thereof with the longitudinal axis of said cylinder disposed in a horizontal plane, a bearing formed through the center of said crankcase with the axis thereof being disposed in a vertical plane, a piston slidably mounted in said cylinder, and a connecting rod operatively connected at one end thereof to said piston, said connecting rod having a bearing formed therein at the other end thereof with the axis of said bearing disposed in a vertical plane, a stator mounted on the concave side of said stator support, said stator sufpport having a bearing formed through the center thereof with the axis of said bearing lying in a vertical plane, a rotor, a shaft, an eccentric, said rotor and said eccentric rigidly mounted to said shaft between the ends thereof, said shaft rotatively mounted at the ends thereof in the crankcase and the stator support bearings, said rotor and said eccentric further positioned on said shaft so that said connecting rod bearing cooperates with said eccentric and; said rotor cooperates with said stator, said shaft further formed with a hole extending axially through the center of said shaft, pump means disposed at the lower end of said shaft for pumping said lubricating oil upwardly through said hole in said shaft, the upper end of said hole through said shaft further being positioned at an angle from the axis of said hole, so that the oil flowing from the top of said hole is given a lateral component of motion when said shaft is rotating, so that said lubricating oil is cooled by the conduction of heat from said oil to said casing while flowing downward along the inner surfaces of said casing, said crankcase further formed to have a depression in a portion of the upper surface thereof directly above said cylinder, said crankcase further being formed to have a hole projecting through said crankcase from said depression into said cylinder, said crankcase further formed to have a second hole projecting therethrough from an upper portion of said depression into said crankcase bearing, said shaft being further formed to have a second hole therethrough, said second hole positioned axially of said second hole in said crankcase and into said first hole in said shaft, whereby said crankcase bearing is lubricated by oil flowing from said second hole in said shaft when said shaft is rotated, and whereby a portion of the oil flowing through said second hole in said shaft is caused to flow through said second hole in said crankcase, whereby said depression is substantially filled with said lubricating oil and fed therefrom through said first hole in said crankcase to lubricate said cylinder.

References Cited in the file of this patent UNITED STATES PATENTS 592,244 Fay Oct. 26, 1897 2,028,584 Bixler Ian. 21, 1936 2,080,236 Steenstrup May 11, 1937 2,133,875 Steenstrup Oct. 18, 1938 2,178,811 Sateren Nov. 7, 1939 2,228,364 Philipp Jan. 14, 1941 2,245,577 Dieckman June 17, 1941 2,463,035 Heitchue Mar. 1, 1949 2,505,709 Goldberg et al. Apr. 25, 1950 2,523,847 Russey Sept. 26, 1950 2,552,166 Gardiner May 8, 1951 2,583,583 Mangan Jan. 29, 1952 2,618,430 Smith Nov. 18, 1952 2,644,635 Warrick et a1. July 7, 1953 

